1. Field of Invention
The invention is directed to anchoring slip assemblies and, in particular, liner hanger devices used for suspending a liner within a wellbore.
2. Description of Art
A liner is a tubular member that is usually run inside of wellbore casing of an oil or gas well and suspended within the wellbore casing. Liners are typically secured within a wellbore by toothed slips that are located on liner hangers. The slips are set by axially translating them with respect to the liner hanger mandrel or housing. As the slips are translated axially, they are cammed radially outwardly by a ramped surface that is fashioned into the mandrel. As the slips move radially outwardly, the toothed surfaces of the slip will bitingly engage the inner wall surface of the wellbore casing. This type of arrangement is shown, for example, in U.S. Pat. No. 4,497,368 in which slips that are radially expanded by riding up over cone elements disposed into the tubular body of the central mandrel.
Actuation systems for such slips in the past employed full circumference hydraulically actuated pistons to move the slips. These designs presented a pressure rating problem in that the full circumference piston frequently had a maximum working pressure significantly lower than the mandrel which it surrounded. Thus, this type of design limited the maximum working pressure in the string to the rating of the cylindrical piston housing assembly. For example, it was not unusual in prior designs to have mandrels rated for 12,000 PSI while the surrounding cylinder housing for the cylindrical piston to only have a rating of approximately 3,000 PSI.
In an effort to improve the shortcoming of this design, another design illustrated in U.S. Pat. No. 5,417,288 was developed. In this design the mandrel body received a pair of bores straddling each of the slips. A piston assembly was mounted in each of the bores with all of the necessary seals. The application of hydraulic pressure in the mandrel into all the piston bores actuated the pistons on either side of each slip through a common sleeve to which all the slips were attached. This design, however, was expensive to manufacture, had many potential leak paths in the form of the ring seals on each of the pistons wherein each slip required two pistons.
On the other hand, this design provided for a higher pressure rating for the liner hanger body and also used the hydraulic pressure directly to actuate the slips. Necessarily it did not include a locking feature against premature slip movements due to inadvertently applied pressures. The design in U.S. Pat. No. 5,417,288 also did not provide for flexibility for changed conditions downhole which could require additional force to set the slips. In essence, each application was designed for a pre-existing set of conditions with field variability not included as a feature of that prior art design.
Additionally, the design of the liner hanger needs to accommodate circulation of mud and cement. The foregoing prior designs, particularly those using a cylindrical piston, obstructed the passages that could have been used for circulating cement and mud.
Slip assemblies in the past also have been configured in a variety of ways. In one configuration, when the slips are actuated, the load is passed through the slips circumferentially through their guides or retainers and transmission of the load to the underlying mandrel is avoided. In other more traditional designs, the slips are driven along tapered surfaces of a supporting cone and the loading is placed on the supporting mandrel is in a radial direction toward its center, thus tending to deform the mandrel when setting the slips. Typical of such applications are U.S. Pat. Nos. 4,762,177, 4,711,326 and 5,086,845.
In another prior attempt, illustrated in U.S. Pat. No. 6,431,277, the slips are designed to move in two directions upon being actuated. The slips initially move in the direction of the actuating piston, but reverse direction through the movement of one or more springs energized to expand in the direction opposite of the actuating piston. The liner hanger in this patent is also designed with a separate spring housing that restricts the total number of springs that can be used and is difficult to assemble.
Also, the liner hanger disclosed in U.S. Pat. No. 6,431,277 does not allow the operator to disassemble the liner hanger in the event that the liner hanger is not set within the wellbore. For example, sometimes the liner hanger must be modified, or repaired, prior to installation. In many instances, the modifications or repairs cannot be accomplished while the liner hanger is “energized” for placement within the wellbore. Therefore, the liner hanger is actuated by activating the piston and the spring and, thus, releasing the slips. Accordingly, before the liner hanger can be installed within the wellbore, the entire liner hanger must be reassembled causing increased downtime and costs.
Further, the liner hanger disclosed in U.S. Pat. No. 6,431,277 utilized a piston having a passageway disposed longitudinally therethrough. The passageway is used to vent and/or oil the piston within the piston housing. As a result, the mass of the piston was lessened which also lessened the amount of energy the piston was capable of releasing upon actuation.
Accordingly, prior to the development of the present invention, there has been no liner hanger that: provides an easy to assemble and disassemble liner hanger; provides a vent port for venting and oiling the piston such that the piston can be solid instead of having a passageway running the length of the piston; and provides an increase in the number of springs use to set the slips of the liner hanger, thereby providing a better initial bite of the slips into the wellbore casing. Therefore, the art has sought a liner hanger that: provides an easy to assemble and disassemble liner hanger; provides a vent port for venting and oiling the piston such that the piston can be solid instead of having a passageway running the length of the piston; and provides an increase in the number of springs use to set the slips of the liner hanger, thereby providing a better initial bite of the slips into the wellbore casing.